1. Field of the Invention
The invention relates to improvements in multipoint strip chart recorders.
2. Description of the Prior Art
Print mechanisms embodying record distinguishing means for multiple point strip chart recorders have been known and employed in industry for many years. Such print mechanisms generally have operated in a single mode, identifying each quantity under measurement by a characteristic mark or color.
Several forms of the prior printing mechanism are illustrated in U.S. Pat. Nos. 2,328,664; 2,525,094 and 2,421,834. Each of these prior printing mechanisms employ a single print wheel mounted on a print carriage, that has a plurality of marking elements on the peripheral portion thereof. When a mark is to be printed, the print wheel is tilted to a precise angle with respect to a chart or other record medium to place a single one of its marking elements in a position to make a mark on this record medium.
The print carriages of some of these prior art multipoint printing mechanisms are mounted for sliding along a spline shaft and are equipped with rollers which ride along a guide rod or channel so that the print carriage can be moved across the top of the chart from one printing position to the other. This rolling action of the roller along the channel has a tendency to produce an undesired amount of static friction due to the sticking-slipping movement between the roller and channel as the print carriage traverses the record medium.
Other more recent recorders mount their print carriage for slidable movement along a stationary rod that extends between and which is fixed to the opposite side of the chassis of these recorders such as is disclosed in my U.S. Pat. No. 3,838,430. Here again, stick-slipping movement of the carriage along a stationary rod takes place that has a tendency to produce undesired static friction between the carriage and the rod on which it is mounted.
Recorders of the aforementioned type employ ink wheels which contain inked pads that are of a different selected color against each one of which a different mark on an associated print wheel is engaged before that mark is brought into printing contact with the record medium.
Each of the ink pads on the ink wheel and the associated marking elements on the print wheel, that are employed in the previously-referred to prior art multi-point offset printing recording devices have a tendency, due to differences in the amount of backlash occurring in their separate gear drives, to move out of color synchronism with one another as their ink pad and print wheels are advanced by their separate indexing gearing and/or pawl and ratchet driving units from one printing position to another.
When a small displacement of the multicolor ink wheel relative to the print wheel takes place, due to gear train backlash, the print wheel characters contact two different color ink pads and thus cause color transfer to occur from one pad to the next. After a relatively short time this action causes the color of the ink in each pad to mix with the color of its adjacent pad. This later action results in a degrading of the colors which the print wheel can then print on the record medium.
Another disadvantage in employing gear trains to drive ink wheels and point wheels is the high cost involved in the manufacture and assemblying of the gears that are used by these gear trains.